Radio base station system method for controlling transmission of synchronization burst and transmission control program

ABSTRACT

In a CS in accordance with a PDMA system, control of transmission of a synchronous burst is performed at a transmission data generating DSP ( 7 ). In particular, the synchronous burst for reconnection is transmitted with a relatively high transmission level during a plurality of first, successive frames and with a relatively low transmission level during a prescribed number of second, successive frames that follow. Such variation in the transmission level is repeated in a certain frame cycle so that an effect of the synchronous burst for reconnection on another PS connected to the CS will be lowered.

TECHNICAL FIELD

[0001] The present invention relates to a radio base station system, anda method and a program of controlling transmission of a synchronousburst. In particular, the present invention relates to a radio basestation system transmitting a synchronous burst for reconnection to auser terminal of which reception signal has been disrupted, as well asto a method and a program for controlling transmission of such asynchronous burst, in a communication system in accordance with a PDMA(Path Division Multiple Access) system in which a plurality of users canestablish spatial multiple access (path multiple access) in one timeslot at the same frequency for data transmission/reception.

BACKGROUND ART

[0002] In recent years, in rapidly developing mobile communicationsystems (for example, Personal Handyphone System, hereinafter referredto as “PHS”), in order to make efficient use of frequencies, a varietyof methods for controlling transmission channel allocation have beenproposed, of which some have been put into practical use.

[0003] In particular, recently, a PDMA system has been proposed toimprove efficiency in the use of radio wave frequencies as mobiletelephones have come into widespread use. In the PDMA system, one timeslot of the same frequency is spatially divided for data transmission ofa plurality of users.

[0004] In the PDMA system, one time slot is spatially divided into aplurality of channels using a mutual interference canceller such as anadaptive array, allowing a plurality of users who will cause littleinterference with each other to establish path multiple access to thetime slot.

[0005] More specifically, in the PDMA system, a cell station(hereinafter, referred to as a “CS”) separates and extracts a multiplestreams of signal waves from personal stations (hereinafter, referred toas a “PS”) of a plurality of users who have established path multipleaccess to channels of the same frequency and the same time slot, usingwell-known adaptive array processing.

[0006]FIG. 9 schematically shows path multiple access state between a CSand PSs in the PDMA system. Referring to FIG. 9, assume that, forexample, three PSs, that is, a PS 10 of a user A, a PS 20 of a user Band a PS 30 of a user C have initially established path multiple accessto a CS 100.

[0007] Here, if PS 10 is disconnected from CS 100, as shown by an arrow(X) for a reason such as movement of user A out of area or deteriorationof a transmission path due to interference and the like, PS 10 will tryto establish a connection with another CS 200 (what is called“handover”), as shown by a dashed line and an arrow (Y).

[0008] Meanwhile, the previous connection target CS 100, that no longercan receive a radio wave from PS 10, transmits at a prescribed level, asynchronous burst for reestablishing connection to PS 10, that is, asynchronous burst for reconnection, for a period of several tens ofseconds, as schematically shown by an arrow (Z).

[0009] If PS 10 was not able to establish connection to CS 200 for somereason, PS 10 will try to recover connection with CS 100. The abovedescribed synchronous burst for reconnection serves as a mark in such acase. Therefore, if PS 10 can recognize the synchronous burst forreconnection (Z), PS 10 will re-establish synchronization with CS 100,and moreover, re-establish a communication channel with CS 100 through aprescribed sequence. On the other hand, if PS 10 was not able torecognize the synchronous burst for reconnection (Z), PS 10 cannotre-establish synchronization with CS 100, and fails in connection withany CS. Consequently, the communication channel is disconnected.

[0010] Here, generally, when a connection between a CS and a PS has beenestablished, a radio wave is transmitted from the CS to the PS withtransmission directivity through well-known adaptive array processing,and the radio wave will not interfere with other PSs that haveestablished multiple access to the CS. As described in the example ofFIG. 9, however, for example, while PS 10 has been disconnected from CS100 for handover to CS 200 for a period of several seconds or severaltens of seconds, CS 100 is not receiving a signal wave from PS 10, andtransmission directivity to PS 10 has been lost. In other words, thesynchronous burst for reconnection transmitted at a prescribed levelwithout transmission directivity to PS 10 for several tens of seconds issimply a disturbance wave (an interfering wave) for respective PSs 20and 30 of other users B and C that have established path multiple accessto CS 100.

[0011] Therefore, transmission from the CS, of the synchronous burst forreconnection without directivity for a long period of time will have anadverse effect on radio waves of other PSs connected to the CS.

[0012] Thus, an object of the present invention is to provide a radiobase station system capable of alleviating an effect of a synchronousburst for reconnection on other PSs that have established multipleaccess to the CS, and capable of easily recovering connection of the PSto the CS, that has failed in handover, as well as to provide a methodand a program for controlling transmission of such a synchronous burst.

DISCLOSURE OF THE INVENTION

[0013] According to the present invention, a radio base station systemtransmitting and receiving a signal to and from a plurality of mobileterminals establishing path multiple access through a plurality ofspatially-divided channels, includes synchronous burst transmissionmeans and synchronous burst transmission level set means. Thesynchronous burst transmission means transmits a synchronous burst forreconnection for each signal frame through a disconnected channel whenpath multiple access to any of the plurality of mobile terminals isdisconnected. The synchronous burst transmission level set means sets atransmission level of the synchronous burst for reconnection to arelatively high level in a plurality of first, successive frames; sets atransmission level of the synchronous burst for reconnection to arelatively low level in a plurality of second, successive frames; andperiodically repeats setting of the transmission level in a frame cycleformed by the plurality of first, successive frames and the plurality ofsecond, successive frames.

[0014] Preferably, the synchronous burst transmission means transmits,in a time-divided manner, for respective mobile terminals, a synchronousburst for reconnection having a transmission level set in the framecycle, when there are a plurality of mobile terminals having pathmultiple access disconnected.

[0015] More preferably, the relatively low level is set to zero level.

[0016] More preferably, the radio base station system further includestransmission level modifying means for lowering a transmission level foranother mobile terminal among the plurality of mobile terminals duringtransmission of the synchronous burst for reconnection by thesynchronous burst transmission means.

[0017] According to another aspect of the present invention, a method ofcontrolling transmission of a synchronous burst in a radio base stationsystem transmitting and receiving a signal to and from a plurality ofmobile terminals establishing path multiple access through a pluralityof spatially-divided channels, includes the steps of: transmitting asynchronous burst for reconnection for each signal frame through adisconnected channel when path multiple access to any of the pluralityof mobile terminals is disconnected; and setting a transmission level ofthe synchronous burst for reconnection to a relatively high level in aplurality of first, successive frames, setting a transmission level ofthe synchronous burst for reconnection to a relatively low level in aplurality of second, successive frames, and periodically repeatingsetting of the transmission level in a frame cycle formed by theplurality of first, successive frames and the plurality of second,successive frames.

[0018] Preferably, in the step of transmitting the synchronous burst,when there are a plurality of mobile terminals having path multipleaccess disconnected, the synchronous burst for reconnection having atransmission level set in the frame cycle is transmitted in atime-divided manner for respective mobile terminals.

[0019] More preferably, the relatively low level is set to zero level.

[0020] More preferably, the method of controlling transmission of thesynchronous burst further includes the step of lowering a transmissionlevel for another mobile terminal among the plurality of mobileterminals during transmission of the synchronous burst for reconnection.

[0021] According to yet another aspect of the present invention, aprogram for controlling transmission of a synchronous burst in a radiobase station system transmitting and receiving a signal to and from aplurality of mobile terminals establishing path multiple access througha plurality of spatially-divided channels, causes a computer to executethe steps of: transmitting a synchronous burst for reconnection for eachsignal frame through a disconnected channel when path multiple access toany of the plurality of mobile terminals is disconnected; and setting atransmission level of the synchronous burst for reconnection to arelatively high level in a plurality of first, successive frames,setting a transmission level of the synchronous burst for reconnectionto a relatively low level in a plurality of second, successive frames,and periodically repeating setting of the transmission level in a framecycle formed by the plurality of first, successive frames and theplurality of second, successive frames.

[0022] Preferably, in the step of transmitting the synchronous burst,when there are a plurality of mobile terminals having path multipleaccess disconnected, the synchronous burst for reconnection having atransmission level set in the frame cycle is transmitted in atime-divided manner for respective mobile terminals.

[0023] More preferably, the relatively low level is set to zero level.

[0024] More preferably, the program for controlling transmission of thesynchronous burst further causes a computer to execute the step oflowering a transmission level for another mobile terminal among theplurality of mobile terminals during transmission of the synchronousburst for reconnection.

[0025] Therefore, according to the present invention, the synchronousburst for reconnection is not transmitted continuously at a constanttransmission level, but transmitted in a certain cycle, in which periodsof high or low (or zero level) transmission level are alternatelyrepeated. Thus, an effect of the synchronous burst for reconnection onother mobile terminals (PS) connected to the radio base station (CS) canbe alleviated.

[0026] In addition, in the present invention, the transmission level toother mobile terminals that have established path multiple access to theradio base station is lowered during transmission of the synchronousburst for reconnection. Thus, a transmission radio wave to other mobileterminals can be prevented from being a disturbance wave for thesynchronous burst for reconnection.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027]FIG. 1 schematically shows an arrangement of transmission slots ina communication system in accordance with a PDMA system.

[0028]FIGS. 2A and 2B show signal formats transmitted between a PS and aCS.

[0029]FIG. 3 is a functional block diagram showing a configuration of aCS in accordance with the PDMA system according to an embodiment of thepresent invention.

[0030]FIG. 4 is a timing chart illustrating a principle of the presentinvention.

[0031]FIG. 5 is a flowchart illustrating a process before startingtransmission of a synchronous burst for reconnection.

[0032]FIG. 6 is a flowchart illustrating a process for controlling atransmission level of the synchronous burst for reconnection.

[0033]FIG. 7 is a flowchart illustrating control of a transmission levelto another PS connected to a CS.

[0034]FIG. 8 is a flowchart illustrating another example of a processfor controlling a transmission level of a synchronous burst forreconnection.

[0035]FIG. 9 schematically shows path multiple access state between a CSand PSs in the PDMA system.

BEST MODES FOR CARRYING OUT THE INVENTION

[0036] In the following, embodiments of the present invention will bedescribed in detail with reference to the figures. It is noted that thesame reference characters refer to the same or corresponding componentsin the figures, and description thereof will not be repeated.

[0037]FIG. 1 schematically shows an arrangement of transmission slotsfor an up link (PS to CS) and a down link (CS to PS) in a communicationsystem in accordance with the PDMA system.

[0038] In FIG. 1, the up link and the down link transmit data in unitsof four slots in a time-sequentially alternate manner, respectively.Both up and down links have the same format.

[0039] A control channel (hereinafter, referred to as “CCH”) isallocated to any given one slot (here, a first slot is assumed). Users 1and 4 establish path multiple access to a slot 2 of next frequency f1,users 2 and 5 establish the same to a slot 3 of a frequency f2, andusers 3 and 6 establish the same to a slot 4 of the last frequency f3.

[0040] In a PHS standard, for example, a signal format per user,transmitted between the CS and the PS of each user connected to eachtime slot of the CS in FIG. 1 is as shown in FIGS. 2A and 2B.

[0041] In other words, a communication channel between the CS and eachPS connected thereto includes a signaling control channel (hereinafter,referred to as “SCCH”) and a traffic channel (hereinafter, referred toas “TCH”) having physical slot arrangements in both up and down linksthereof, as respectively shown in FIGS. 2A and 2B.

[0042] More specifically, the SCCH includes: R (ramp time for transientresponse) of 4 bits; SS (start symbol) of 2 bits; PR (preamble) of 62bits; UW (unique word) of 32 bits; CI (channel identification) of 4bits; CSID (CS identification code) of 42 bits; PSID (PS identificationcode) of 28 bits; I (up/down idle bit) of 34 bits; CRC (cyclicredundancy check) of 16 bits; and G (guard bit) of 16 bits.

[0043] Among the above, CI (4 bits), CSID (42 bits), PSID (28 bits), I(34 bits) and CRC (16 bits) constitute a synchronous burst in eachup/down link.

[0044] Meanwhile, the TCH includes: R of 4 bits; SS of 2 bits; PR of 6bits; UW of 16 bits; CI of 4 bits; SS of 16 bits; I of 160 bits; CRC of16 bits; and G of 16 bits.

[0045] The SCCH shown in FIG. 2A is used for activating the TCH shown inFIG. 2B, to establish a traffic channel.

[0046] Note that a total of 8 slots shown in FIG. 1 constitutes oneframe for a transmission signal. Each slot has a time length of 625microseconds, and therefore, one frame has a time length of fivemilliseconds.

[0047] Next, FIG. 3 is a functional block diagram showing aconfiguration of the CS in accordance with the PDMA system in anembodiment of the present invention.

[0048] As described in conjunction with FIGS. 2A and 2B, a signal wavecommunicated between the CS and the PS includes the control channel SCCHtransmitting information necessary for call connection and the trafficchannel TCH used for communication.

[0049] Referring to FIG. 3, a multiple streams of reception signal wavesfrom a plurality of not-shown PSs, received by an array antenna 1 formedby a plurality of not-shown antennas, are subjected to a prescribedreception processing such as amplification, frequency conversion and thelike at a reception RF amplifier 2. Thereafter, the signal waves areconverted to digitally demodulated signals by a demodulator 3, andsupplied to a digital signal processor (DSP) 4 for reception dataprocessing.

[0050] In DSP 4, the digitally demodulated signals are subjected to avariety of processings by software, including well-known adaptive arrayprocessing. Then, reception signals of respective users are separatedand extracted by Weight vectors calculated for respective users. Theseparated and extracted reception signals from respective users areconnected to a public network 6 through a public network interface I/F5.

[0051] Meanwhile, a transmission signal from public network 6 isprovided to a DSP 7 for generating transmission data through publicnetwork I/F 5. The weight vectors for respective users calculated by DSP4 for reception data processing are provided to DSP 7 for generatingtransmission data; and transmission directivities of respective usersare determined.

[0052] Digital transmission data generated in DSP 7 for generatingtransmission data is modulated to an analog transmission signal in amodulator 8, and provided to a transmission RF amplifier 9. TransmissionRF amplifier 9 performs transmission processing to a multiple streams oftransmission signals, and transmits the signals with transmissiondirectivity to the PS of a corresponding user through array antenna 1.

[0053] Next, FIG. 4 is a timing chart showing a principle of the presentinvention, and FIGS. 5 to 8 are flowcharts showing control oftransmission of a synchronous burst for reconnection by a CS accordingto the embodiment of the present invention shown in FIG. 3.

[0054] As described previously, conventionally, when a PS tries toswitch a connection target to another CS because the PS moves out ofarea of the previous CS or because there is an interference on atransmission path, the previous CS transmits, at a prescribed level, adown (CS to PS) synchronous burst for reconnection for a prescribed timeperiod in a channel that has been used for communication with the PS.This, however, resulted in a disturbance wave (an interfering wave) forother PSs connected to the CS.

[0055] The CS according to the embodiment of the present inventiontransmits the synchronous burst for reconnection, not at a constantlevel continuously for a prescribed time period, but with differenttransmission levels in a certain cycle, so as to lower an effect of thesynchronous burst for reconnection on other PSs.

[0056] An example of a control step in the embodiment will be describedbelow with reference to FIGS. 4 to 7. As shown in FIG. 4, it is assumedthat one cycle is formed by 240 frames (one frame is 5 millisecondslong, and 240 frames are 1.2 seconds long). A down synchronous burst istransmitted with a relatively high level during successive first eightframes, and with a relatively low level during remaining successive 232frames. If the relatively low level is set to zero, the synchronousburst will be transmitted only during first eight frames, and nottransmitted during remaining 232 frames. Thus, an intermittent operationis realized.

[0057] As shown in FIG. 4, such variation in transmission levels isrepeated in a cycle of 240 frames, thereby lowering an effect of thesynchronous burst for reconnection on other PSs, as compared with anconventional example, in which the down synchronous burst is transmittedfor reconnection on a constant transmission level in successive framesfor several tens of seconds.

[0058] Such transmission control of the synchronous burst is realized bysoftware in DSP 7 for generating transmission data of the CS shown inFIG. 3.

[0059] Next, referring to FIGS. 5 to 7, control of transmission of thesynchronous burst for reconnection by DSP 7 for generating transmissiondata will be described in detail.

[0060]FIG. 5 is a flowchart showing control steps that take place whenthe CS in FIG. 4 first detects switching of the PS of one user toanother CS (TCH switch) for some reason, and starts transmission of thesynchronous burst for reconnection.

[0061] Referring to FIG. 5, when control starts in step S1, whether ornot the CS has received a TCH switch request requesting switching of aPS of one user to another CS, that is, TCH switch, is determined in stepS2. When it is determined that the CS has received the request, theprocess will proceed to step S5, where the CS transmits to the PS, aninstruction for TCH switch.

[0062] Meanwhile, when it is determined in step S2 that the request forTCH switch has not been received, the process will proceed to step S3,where the CS determines whether a condition for TCH switch is satisfiedor not. When it is determined that the condition for TCH switch issatisfied, the process will proceed to step S5, where the CS transmitsto the PS, an instruction for TCH switch. In step S3, when it isdetermined that the condition for TCH switch is not satisfied, theprocess will end at step S4.

[0063] When the instruction for TCH switch is transmitted in step S5,the process will proceed to S6, where a switch wait timer is initializedto zero. Then, whether or not the PS actually performed TCH switch isdetermined in step S9, while a count of the switch wait timer ismonitored in step S7.

[0064] When it is determined that TCH switch has not been performed,steps S7 and S9 as described above are repeated, while the value of thetimer is incremented in step S11. Meanwhile, when it is determined instep S9 that the PS has performed TCH switch, the process will proceedto step S10, where transmission of the synchronous burst forreconnection is started. Control of a transmission level of thesynchronous burst for reconnection will be described below. The processwill end at step S12.

[0065] As a result of repeating steps S7, S9 and S11 as described above,when it is determined in step S7 that the count value of switch waittimer reaches a prescribed value, that is, time-out, it is determinedthat the PS did not actually perform TCH switch. The process will end atstep S8, without transmitting the synchronous burst for reconnection.

[0066] Next, FIG. 6 is a flowchart showing a control process, in which,after the instruction is given in step S10 of FIG. 5, to starttransmission of the synchronous burst for reconnection, the CS controlsa transmission level of the synchronous burst for reconnection in acycle of 240 frames as shown in FIG. 4.

[0067] Referring to FIG. 6, when control starts in step S21, whether ornot the instruction has been given to start transmission of thesynchronous burst for reconnection in the frame is determined in stepS22. If the instruction for transmission has not been given, a framecounter counting the number of frames is initialized to zero in stepS23, and the process will end at step S24.

[0068] Meanwhile, if the instruction for transmission has been given,the frame counter is incremented by one corresponding to the frame instep S25. Whether or not the value of the frame counter is equal to orgreater than 240 in the frame is determined in step S26. If the value isdetermined to be equal to or greater than 240, the frame counter isinitialized to zero in step S27.

[0069] Then, the process will proceed to step S28, and whether or notthe value of the frame counter is equal to or greater than eight isdetermined. In the frame, since the frame counter has been justinitialized to zero in step S27, the value for the frame counter is lessthan eight. Therefore, the process will proceed to step S29, where thesynchronous burst will be transmitted with a relatively hightransmission level in the frame. The process of the frame will end atstep S31.

[0070] The process of FIG. 6 is repeated for each frame, and thesynchronous burst will be transmitted with a relatively hightransmission level in step S29 during successive eight frames (framecounter value 0 to 7) until the value for the frame counter reacheseight in step S28.

[0071] Thereafter, if it is determined in step S28 that the value forthe frame counter is equal to or greater than eight in a certain frame,the process will proceed to step S30, and the synchronous burst istransmitted with a relatively low level (or zero level) in the frame.The process of the frame will end at step S31.

[0072] The process of FIG. 6 is further continued for each frame, andthe synchronous burst will be transmitted with a relatively lowtransmission level in step S30 during successive 232 frames (framecounter value 8 to 231) as shown in FIG. 4 until the value for the framecounter reaches 240 in step S26.

[0073] Thereafter, if it is determined in step S26 that the value forthe frame counter is equal to or greater than 240 in a certain frame,the frame counter is again initialized to zero in step S27. Thesynchronous burst will be transmitted with a relatively low transmissionlevel (or zero level) in step S29 further during successive eightframes, as shown in FIG. 4, until the value for the frame counterreaches eight in step S28.

[0074] As described above, using control of transmission of thesynchronous burst shown in FIG. 6, there are periods during whichtransmission level of the synchronous burst for reconnection is high orlow (or at zero level) in a certain frame cycle, as shown in the timingchart of FIG. 4. Therefore, an effect as an interfering wave of thesynchronous burst for reconnection on other PSs connected to the CS canbe lowered.

[0075] On the other hand, a transmission wave for other PSs connected tothe CS is also regarded as a disturbance wave for the above describedsynchronous burst for reconnection. Therefore, a transmission leveltoward other PSs during transmission of the synchronous burst forreconnection should be lowered so that the disconnected PS can easilyrecognize a burst for reconnection to establish reconnection with theCS.

[0076]FIG. 7 is a flowchart showing a transmission control process ofDSP 7 controlling a transmission level to other PSs when transmitting asynchronous burst for reconnection in such a manner.

[0077] Referring to FIG. 7, when the process starts in step S41, whetheror not a user to which the synchronous burst with a high transmissionlevel is supplied is present among the remaining users that haveestablished path multiple access to the same slot is determined in stepS42.

[0078] If such a user is not present, the process will end at step S45.On the other hand, if it is determined in step S42 that a user with hightransmission level is present, the process for lowering the transmissionlevel is performed in step S43. Then, the process will end at step S45.

[0079] Thus, an adverse effect as an interfering wave, caused dependenton a transmission level to other users that have established pathmultiple access, on the synchronous burst for reconnection can beprevented, and the disconnected PS can easily recover connection to theCS.

[0080] When controlling transmission of the synchronous burst shown inFIG. 6, as described in conjunction with FIG. 1, it was assumed that thenumber of users that have established multiple access in each slot wastwo, and that control of transmission of the synchronous burst forreconnection was performed for one of the two users. Meanwhile, forexample, if three or more users have established multiple access to eachslot, and moreover, for two or more users among them, the synchronousbursts for reconnection are simultaneously transmitted, transmissioncycles thereof may overlap. If the transmission cycles of two or moresynchronous bursts for reconnection without transmission directivityoverlap, it will be difficult for a corresponding PS to accuratelyrecognize the synchronous burst for reconnection and to establishreconnection to the CS.

[0081]FIG. 8 is a flowchart showing a process for controlling atransmission level of a synchronous burst for reconnection in suchmultiple access state. In the process of FIG. 6, a frame countercounting 240 frames, that is, one process cycle, and a frame countercounting eight frames during which the transmission level is set highare employed. In an example of FIG. 8, however, only one frame counteris provided, and sequentially defines a time period during which eachuser transmits with a high transmission level.

[0082] For example, when the synchronous burst for reconnection istransmitted respectively to four users that have established multipleaccess, for user number 0, the transmission level is set high for aperiod of frame 0 to 7 of 240 frames provided as one cycle, and is setlow for a period of frame 8 to 239. Next, for user number 1, thetransmission level is set high for a period of frame 60 to 67, and isset low for a period of frame 0 to 59 and 68 to 239. Next, for usernumber 2, the transmission level is set high for a period of frame 120to 127, and is set low for a period of frame 0 to 119 and 128 to 239.Next, for user number 3, the transmission level is set high for a periodof frame 180 to 187, and is set low for a period of frame 0 to 179 and188 to 239.

[0083] The process will be specifically described with reference to FIG.8. When control starts in step S51, whether or not an instruction fortransmission of a synchronous burst for reconnection has been given inthe frame is determined in step S52. If the instruction has not beengiven, the frame counter is incremented by one in step S57, and theprocess will end at step S58.

[0084] Meanwhile, if the instruction has been given, “tmp” is given instep S53, which is a value obtained by multiplying a user number by thenumber of frames. Here, the number of frames is obtained by dividing240, which is the number of frames for one cycle, by the number of usersthat have established multiple access.

[0085] In the example where four users have established multiple accessas described above, tmp for user number 0 is 0; tmp for user number 1 is60; tmp for user number 2 is 120; and tmp for user number 3 is 180.

[0086] For example, if user number is 0, whether or not the value of theframe counter is equal to or greater than tmp=0 and less than tmp+8=8 isdetermined in step S54. For user number 0, as the transmission level isset high during this frame period as described above, the process willproceed to step S55, where the synchronous burst for reconnection foruser number 0 will be transmitted with a relatively high transmissionlevel.

[0087] On the other hand, if the value of the frame counter is not inthe above range, the process will proceed to step S56, where thesynchronous burst for reconnection for user number 0 will be transmittedwith a relatively low transmission level.

[0088] After the synchronous burst is transmitted in steps S55 or S56,the frame counter is incremented by one in step S57, and the processwill end at step S58.

[0089] Next, for user number 1, whether or not the value of the framecounter is equal to or greater than tmp=60 and less than tmp+8=68 isdetermined in step S54. For user number 1, as the transmission level isset high during this frame period as described above, the process willproceed to step S55, where the synchronous burst for reconnection foruser number 1 will be transmitted with a relatively high transmissionlevel.

[0090] On the other hand, if the value of the frame counter is not inthe above range, the process will proceed to step S56, where thesynchronous burst for reconnection for user number 1 will be transmittedwith a relatively low transmission level.

[0091] Next, for user number 2, whether or not the value of the framecounter is equal to or greater than tmp=120 and less than tmp+8=128 isdetermined in step S54. For user number 2, as the transmission level isset high during this frame period as described above, the process willproceed to step S55, where the synchronous burst for reconnection foruser number 2 will be transmitted with a relatively high transmissionlevel.

[0092] On the other hand, if the value of the frame counter is not inthe above range, the process will proceed to step S56, where thesynchronous burst for reconnection for user number 2 will be transmittedwith a relatively low transmission level.

[0093] Next, for user number 3, whether or not the value of the framecounter is equal to or greater than tmp=180 and less than tmp+8=188 isdetermined in step S54. For user number 3, as the transmission level isset high during this frame period as described above, the process willproceed to step S55, where the synchronous burst for reconnection foruser number 3 will be transmitted with a relatively high transmissionlevel.

[0094] On the other hand, if the value of the frame counter is not inthe above range, the process will proceed to step S56, where thesynchronous burst for reconnection for user number 3 will be transmittedwith a relatively low transmission level.

[0095] Note that, for the PS being connected to the CS, control of FIG.7 as previously described is performed.

[0096] As described above, in controlling transmission shown in FIG. 8,when a synchronous burst for reconnection is transmitted to four usersamong those who have established multiple access, for each user, controlby varying the transmission levels (high transmission level for eightframes, and low transmission level for 232 frames) in a 240 frame cycleas in the example of FIG. 6 is performed in a sequential, time-dividedmanner, with a cycle shifted from that of other users by 60 frames each.Thus, the transmission cycles of the synchronous burst can be preventedfrom overlapping among users, and the disconnected PS can easily recoverconnection to the CS.

[0097] As described above, according to the present invention, periodsduring which a synchronous burst for reconnection has high or lowtransmission level are alternately provided in a certain cycle.Therefore, an effect of the synchronous burst for reconnection as aninterfering wave on other mobile terminals (PS) that have establishedpath multiple access to the mobile base station (CS) can be lowered.

[0098] In addition, in the present invention, during a transmissionperiod of the synchronous burst for reconnection, control is performedso that the transmission level to other PSs that have established pathmultiple access to the. CS is lowered, whereby the disconnected PS caneasily establish reconnection to the CS.

INDUSTRIAL APPLICABILITY

[0099] According to the present invention, a synchronous burst forreconnection will not have an effect as an interfering wave on othermobile terminals that have established path multiple access to a radiobase station. Therefore, the present invention is effective in a radiobase system transmitting and receiving a signal to and from a pluralityof mobile terminals that have established path multiple connectionthrough a plurality of spatially-divided channels.

1. A radio base station system transmitting and receiving a signal toand from a plurality of mobile terminals establishing path multipleaccess through a plurality of spatially-divided channels, comprising:synchronous burst transmission means (7) for transmitting a synchronousburst for reconnection for each signal frame through a disconnectedchannel when path multiple access to any of said plurality of mobileterminals is disconnected; and synchronous burst transmission level setmeans (7) for setting a transmission level of said synchronous burst forreconnection to a relatively high level in a plurality of first,successive frames, setting a transmission level of said synchronousburst for reconnection to a relatively low level in a plurality ofsecond, successive frames, and periodically repeating setting of thetransmission level in a frame cycle formed by said plurality of first,successive frames and said plurality of second, successive frames. 2.The radio base station system according to claim 1, wherein saidsynchronous burst transmission means transmits, in a time-dividedmanner, for respective mobile terminals, a synchronous burst forreconnection having a transmission level set in said frame cycle, whenthere are a plurality of mobile terminals having path multiple accessdisconnected.
 3. The radio base station system according to claim 1,wherein said relatively low level is set to zero level.
 4. The radiobase station system according to claim 1, further comprisingtransmission level modifying means for lowering a transmission level foranother mobile terminal among said plurality of mobile terminals duringtransmission of said synchronous burst for reconnection by saidsynchronous burst transmission means.
 5. A method of controllingtransmission of a synchronous burst in a radio base station systemtransmitting and receiving a signal to and from a plurality of mobileterminals establishing path multiple access through a plurality ofspatially-divided channels, comprising the steps of: transmitting asynchronous burst for reconnection for each signal frame through adisconnected channel when path multiple access to any of said pluralityof mobile terminals is disconnected; and setting a transmission level ofsaid synchronous burst for reconnection to a relatively high level in aplurality of first, successive frames, setting a transmission level ofsaid synchronous burst for reconnection to a relatively low level in aplurality of second, successive frames, and periodically repeatingsetting of the transmission level in a frame cycle formed by saidplurality of first, successive frames and said plurality of second,successive frames.
 6. The method according to claim 5, wherein in saidstep of transmitting the synchronous burst, when there are a pluralityof mobile terminals having path multiple access disconnected, thesynchronous burst for reconnection having a transmission level set insaid frame cycle is transmitted in a time-divided manner for respectivemobile terminals.
 7. The method according to claim 5, wherein saidrelatively low level is set to zero level.
 8. The method according toclaim 5, further comprising the step of lowering a transmission levelfor another mobile terminal among said plurality of mobile terminalsduring transmission of said synchronous burst for reconnection.
 9. Aprogram for controlling transmission of a synchronous burst in a radiobase station system transmitting and receiving a signal to and from aplurality of mobile terminals establishing path multiple access througha plurality of spatially-divided channels, causing a computer to executethe steps of: transmitting a synchronous burst for reconnection for eachsignal frame through a disconnected channel when path multiple access toany of said plurality of mobile terminals is disconnected; and setting atransmission level of said synchronous burst for reconnection to arelatively high level in a plurality of first, successive frames,setting a transmission level of said synchronous burst for reconnectionto a relatively low level in a plurality of second, successive frames,and periodically repeating setting of the transmission level in a framecycle formed by said plurality of first, successive frames and saidplurality of second, successive frames.
 10. The program according toclaim 9, wherein in said step of transmitting the synchronous burst,when there are a plurality of mobile terminals having path multipleaccess disconnected, the synchronous burst for reconnection having atransmission level set in said frame cycle is transmitted in atime-divided manner for respective mobile terminals.
 11. The programaccording to claim 9, wherein said relatively low level is set to zerolevel.
 12. The program according to claim 9, further comprising the stepof lowering a transmission level for another mobile terminal among saidplurality of mobile terminals during transmission of said synchronousburst for reconnection.